1. Field of the Invention
The present invention relates to an actuator using a strain element having such a property that it is deformed when voltage is applied, the so-called piezoelectric inverse effect, and a method of manufacturing the strain element.
2. Description of the Related Art
Conventionally, there has been an actuator using a piezoelectric element having such a property that a strain occurs and a deformation is caused when voltage is applied, the so-called piezoelectric inverse effect. In the actuator using the piezoelectric element, since an amount of deformation (amount of displacement) of the piezoelectric element is small, a mechanism portion (displacement enlargement mechanism portion) for enlarging the amount of displacement must be provided, and there has been a problem that its main body becomes large, and a problem that it takes labor to assemble the displacement enlargement mechanism portion.
Incidentally, the displacement enlargement mechanism portion is, as disclosed in Japanese Patent Unexamined Publication No. Hei. 4-25640, a mechanical enlargement mechanism portion employing the principle of leverage, a liquid type enlargement mechanism portion employing Pascal""s principle, or the like.
Recently, an actuator in which the displacement enlargement mechanism portion is constructed by an actuator itself is proposed (Japanese Patent Unexamined Publication No. Hei. 6-216424). This actuator is constructed such that a belt-shaped piezoelectric element is helically wound over the full length of a hollow coil spring. According to this actuator, when voltage is applied to the piezoelectric element, a torsion moment by the deformation of the piezoelectric element acts on the full length of the coil spring, so that the coil spring is displaced in the axial direction. The amount of displacement of the coil spring in the axial direction can be made large if the number of turns of the coil spring is increased.
However, the actuator is assembled by helically winding the belt-shaped piezoelectric element over the full length of the hollow coil spring, and the step of helically winding the belt-shaped piezoelectric element is a very troublesome step, so that manufacturing costs are raised and the actuator is expensive.
An object of the present invention is to provide a small and inexpensive actuator which has a simple structure and can obtain a large displacement, and a method of manufacturing a strain element applied to the actuator.
The actuator of the present invention has the following structure to solve the above problem.
(1) An actuator comprises a strain element having a property of a piezoelectric inverse effect, in which the strain element is wound like a coil, and electrodes are formed on an inner circumferential surface and an outer circumferential surface.
According to this structure, when voltage is applied between the electrodes formed on the inner circumferential surface and the outer circumferential surface, the strain element wound like the coil is displaced in a direction to contract or expand the diameter of the coil. At this time, if one end portion of the strain element wound like the coil is fixed, the other end portion, which is not fixed, is rotated in accordance with the contraction or expansion of the diameter. The rotation direction at this time is determined by the winding direction of the strain element, and the rotation amount of the other end portion is determined by the number of turns of the strain element or the like.
Accordingly, since the displacement of sufficient magnitude can be easily obtained by adjusting the number of turns or the like, a displacement enlargement mechanism portion is also not required.
Besides, the strain element having the shape wound like the coil can be easily formed by extrusion molding or the like, and formation of the electrodes on the inner circumferential surface and the outer circumferential surface of the strain element can be easily carried out by a well-known processing method such as a printing or plating method. Accordingly, the actuator of this invention does not require a troublesome step in its manufacturing process and can be formed inexpensively.
(2) An actuator comprises a strain element having a property of a piezoelectric inverse effect, in which a metal coil wound like a coil is provided, the strain element is formed on at least one of an inner circumferential surface and an outer circumferential surface of the metal coil, and an electrode is formed on a surface of the strain element.
According to this structure, the strain element is formed on one of or both of the inner circumferential surface and the outer circumferential surface of the metal coil wound like the coil. The electrode is formed on the surface of the strain element. When voltage is applied between the electrode and the metal coil, in accordance with the displacement of the strain element, the metal coil is deformed in a direction to contract or expand the diameter of the coil. Accordingly, similarly to the above structure (1), if one end portion of the metal coil is fixed, the other end portion which is not fixed is rotated.
Besides, when well-known hydrothermal synthesis is used, the strain element can be easily formed on the outer circumferential surface or the inner circumferential surface of the metal coil wound like the coil. Besides, formation of the electrode on the surface of the strain element (the surface here is a surface at a side opposite to a contact surface to the metal coil) can also be easily performed by a well-known method such as a printing or plating method.
Incidentally, as compared with a case where the strain element is formed on only one of the inner circumferential surface and the outer circumferential surface of the metal coil wound like the coil, when the strain element is formed on both the inner circumferential surface and the outer circumferential surface, the displacement of the metal coil becomes large, so that further miniaturization can be realized.
(3) An actuator provided with a strain element having a property of a piezoelectric inverse effect, in which the strain element is wound like a coil, an electrode having a width narrower than a width of the strain element is formed on an upper surface of the strain element along a side portion of one of an inner circumferential side and an outer circumferential side, and an electrode having a width narrower than the width of the strain element is formed on a lower surface of the strain element along a side portion of an opposite side of that of the upper surface.
According to this structure, the electrode having the width narrower than the strain element is formed on the upper surface of the strain element wound like the coil along the side portion of one of the inner circumferential side and the outer circumferential side, and the electrode having the width narrower than the strain element is formed on the lower surface of the strain element along the side portion of the opposite side of that of the upper surface. With respect to two electrodes arranged side by side, since a desirable shape is such that all of them are formed on the strain element, it is appropriate that the width of the electrode is made not larger than half of the width of the strain element. However, even if the electrode has a size exceeding the half so that it protrudes to the outside or inside of the strain element, there does not especially arise a problem.
When voltage is applied between the electrodes formed on the upper surface and the lower surface of the strain element, distortion is generated over the full length of the strain element wound like the coil, and displacement occurs in the axial direction. Since the displacement amount in the axial direction at this time can be adjusted by the number of turns of the strain element or the like, the displacement amount of sufficient magnitude can be easily obtained.
Besides, as described above, the strain element wound like the coil can be easily formed by the extrusion molding or the like, and the formation of the electrodes on the inner circumferential surface and the outer circumferential surface of the strain element can also be easily carried out by the printing, plating method or the like.
(4) An actuator provided with a strain element having a property of a piezoelectric inverse effect, in which a metal coil wound like a coil is provided, a strain element having a width narrower than a width of the metal coil is formed on an upper surface of the metal coil along a side portion of one of an inner circumferential side and an outer circumferential side, a strain element having a width narrower than the width of the metal coil is formed on a lower surface of the metal coil along a side portion of an opposite side of that of the upper surface, and electrodes are formed on surfaces of the strain elements.
According to this structure, the strain element having the width narrower than the width of the metal coil is formed on the upper surface of the metal coil along the side portion of one of the inner circumferential side and the outer circumferential side, and the strain element having the width narrower than the width of the metal coil is formed on the lower surface of the metal coil along the side portion of the opposite side of that of the upper surface. The electrodes are formed on the surfaces of the strain elements formed on the upper surface and the lower surface of the metal coil, respectively.
When voltage is applied between the electrode and the metal coil, distortion is generated in the metal coil, and the metal coil is displaced in the axial direction. Since the displacement amount in the axial direction at this time can be adjusted by the number of turns of the metal coil or the like, the displacement amount of sufficient magnitude can be easily obtained.
Besides, as described above, if the well-known hydrothermal synthesis is used, the strain elements can be easily formed on the outer circumferential surface and the inner circumferential surface of the metal coil wound like the coil. Besides, the formation of the electrode on the surface of the strain element (the surface here is a surface at a side opposite to a contact surface to the metal coil) can be easily carried out by the well-known method such as printing or plating method.
(5) An actuator provided with a strain element having a property of a piezoelectric inverse effect, in which a metal coil wound like a coil is provided, two belt-shaped strain elements each having a width of not larger than half of a width of the metal coil are formed side by side on at least one of an upper surface and a lower surface of the metal coil, and electrodes are formed on surfaces of the strain elements.
According to this structure, the two belt-shaped strain elements each having the width of not larger than half of the metal coil are formed side by side on one of or both of the upper surface and the lower surface of the metal coil. Besides, the electrodes are formed on the surfaces of the strain elements. Here, if the polarization directions of the two strain elements formed side by side are made opposite to each other, when voltage is applied between the electrode and the metal coil, distortion is generated in the metal coil, and the metal coil is displaced in the axial direction.
Besides, as compared with a case where two strain elements are formed side by side only on one of the upper surface and the lower surface of the metal coil, when two strain elements are formed side by side on both of the upper surface and the lower surface of the metal coil, the distortion generated when voltage is applied becomes large, so that further miniaturization of the actuator can be realized. Incidentally, the polarization directions of the two strain elements formed side by side on the upper surface and the lower surface are opposite to each other, the polarization directions of the strain element on the upper surface at the outer circumferential side and the strain element on the lower surface at the inner circumferential side are opposite to each other, and the polarization directions of the strain element on the upper surface at the inner circumferential side and the strain element on the lower surface at the outer circumferential side are also opposite to each other.
(6) An actuator provided with a strain element having a property of a piezoelectric inverse effect, in which the strain element is wound like a coil, an electrode having a height lower than a height of the strain element is formed on an inner circumferential surface of the strain element along an end portion of one of an upper end and a lower end, and an electrode having a height lower than the height of the strain element is formed on an outer circumferential surface of the strain element along an opposite end portion of that of the inner circumferential surface.
(7) An actuator provided with a strain element having a property of a piezoelectric inverse effect, in which a metal coil wound like a coil is provided, a strain element having a height lower than a height of the metal coil is formed on an inner circumferential surface of the metal coil along an end portion of one of an upper end and a lower end, a strain element having a height lower than the height of the metal coil is formed on an outer circumferential surface of the metal coil along an opposite end portion of that of the inner circumferential surface, and electrodes are formed on surfaces of the strain elements.
(8) An actuator provided with a strain element having a property of a piezoelectric inverse effect, in which a metal coil wound like a coil is provided, two belt-shaped strain elements each having a height of not larger than half of a height of the metal coil are formed side by side on at least one of an inner circumferential surface and an outer circumferential surface of the metal coil, and electrodes are formed on surfaces of the strain elements.
While the strain elements and the electrodes are formed on the upper surface and the lower surface in the structures (3) to (5), they are formed on the inner circumferential surface and the outer circumferential surface in the structures (6) to (8), and the same effects as those of the structures (3) to (5) can be obtained.
(9) An actuator provided with a strain element having a property of a piezoelectric inverse effect, in which the strain element is belt-shaped, an electrode having a width narrower than a width of the strain element is formed on one surface of the strain element along one side portion, and an electrode having a width narrower than the width of the strain element is formed on the other surface of the strain element along the other side portion.
(10) An actuator provided with a strain element having a property of a piezoelectric inverse effect, in which a belt-shaped metal plate is provided, a strain element having a width narrower than a width of the metal plate is formed on one surface of the metal plate along one side portion, a strain element having a width narrower than the width of the metal plate is formed on the other surface of the metal plate along the other side portion, and electrodes are formed on surfaces of the strain elements.
(11) An actuator provided with a strain element having a property of a piezoelectric inverse effect, in which a belt-shaped metal plate is provided, two belt-shaped strain elements each having a width of not larger than half of the metal coil are formed side by side on at least one surface of the metal plate, and electrodes are formed on surfaces of the strain elements.
In the structures (9) to (11), the coil-shaped strain elements or the coil-shaped metal coils of the structures (3) to (8) are replaced by the belt-shaped strain elements or the belt-shaped metal plates.
(12) An actuator provided with a strain element having a property of a piezoelectric inverse effect, in which both end portions of the strain element are spirally wound, and electrodes are formed on an inner circumferential surface and an outer circumferential surface.
(13) An actuator provided with a strain element having a property of a piezoelectric inverse effect, in which a metal coil having both ends spirally wound, the strain element is formed on at least one of an inner circumferential surface and an outer circumferential surface of the metal coil, and an electrode is formed on a surface of the strain element.
In the structures (12) and (13), since both the ends are spirally wound, when voltage is applied, a displacement can be generated at both the ends.
(14) An actuator provided with a strain element having a property of a piezoelectric inverse effect, in which the strain element is spirally wound, electrodes are formed on an inner circumferential surface and an outer circumferential surface, and a dielectric is provided in parallel with the strain element.
(15) An actuator provided with a strain element having a property of a piezoelectric inverse effect, in which a spirally wound metal coil is provided, the strain element is formed on at least one of an inner circumferential surface and an outer circumferential surface of the metal coil, an electrode is formed on a surface of the strain element, and a dielectric is provided in parallel with the strain element.
According to the structures (14) and (15), since the dielectric connected in parallel with the strain element is provided, when application of voltage to the strain element is turned off, a return to an initial state of the strain element can be restricted by using electric charges stored in the dielectric.
(16) A dielectric is provided in parallel with the strain element.
According to this structure, as described above, the return to the initial state of the strain element can be restricted by using the electric charges stored in the dielectric.
(17) The strain element is a laminated strain element.
According to this structure, since the laminated strain element is used, each piezoelectric element can be made thin. In a bimorph type piezoelectric element, as the thickness becomes small, the displacement becomes large, and the force generated by the displacement becomes weak. Since the plurality of piezoelectric elements are laminated, a large force can be generated when voltage is applied, and a large displacement can be obtained. Accordingly, the actuator can be constructed to be still smaller.
Besides, a method of manufacturing a strain element according to the present invention comprises the following steps.
(1) A coating film of titanium or a titanium compound is formed on a surface of a cylindrical mold, the coating film formed on the surface of the cylindrical mold is shaped like a coil, a crystal film of a strain element having a property of a piezoelectric inverse effect is formed on the coating film shaped like the coil by hydrothermal synthesis, and the strain element is removed from the cylindrical mold.
According to the method of manufacturing the strain element, the crystal film of the strain element is formed by the hydrothermal synthesis on the coating film of the titanium or the titanium compound shaped like the coil on the surface of the cylindrical mold. Accordingly, by removing it from the mold, the strain element can be manufactured into the coil shape. An actuator wound like the coil can be manufactured by forming an electrode on this strain element.
Besides, the coating film of the titanium or the titanium compound is formed on an inner circumferential surface of the removed strain element, and this film functions as an electrode.
(2) A crystal film of a strain element having a property of a piezoelectric inverse effect is formed by hydrothermal synthesis on an inner circumferential surface of the strain element removed from the cylindrical mold, so that laminated coil-shaped strain elements can be manufactured between which the film of the titanium or the titanium compound functioning as the electrode is interposed.
(3) A coating film of titanium or a titanium compound is formed on an outer circumferential surface of the strain element removed from the cylindrical mold, a crystal film of a strain element having a property of a piezoelectric inverse effect is formed by hydrothermal synthesis on the coating film formed on the outer circumferential surface of the strain element, so that similarly to the method (2), laminated coil-shaped strain elements can be manufactured between which the film of the titanium or the titanium compound functioning as the electrode is interposed.
(4) A hydrophilic region is formed into a coil shape on a surface of a cylindrical mold made of a water-repellent resin as a base material, the cylindrical mold is dipped in a solution containing suspended fine particles of a strain element having a property of a piezoelectric inverse effect, the cylindrical mold is pulled up, and the adherent strain element is removed from the cylindrical mold.
According to the above manufacturing method, since the fine particles of the strain element adhere to the hydrophilic region formed into the coil shape on the surface of the cylindrical mold, the strain element wound like the coil can be manufactured by removing them from the mold.
(5) A water-repellent treatment is performed so that a hydrophilic region is formed into a coil shape on a surface of a cylindrical mold made of a hydrophilic resin as a base material, the cylindrical mold is dipped in a solution containing suspended fine particles of a strain element having a property of a piezoelectric inverse effect, the cylindrical mold is picked up, and the adherent strain element is removed from the cylindrical mold.
According to the above manufacturing method as well, similarly to the method (4), since the fine particles of the strain element adhere to the hydrophilic region formed into the coil shape on the surface of the cylindrical mold, the strain element wound like the coil can be manufactured by removing them from the mold.
(6) A hot isostatic press is performed to the cylindrical mold before the adherent strain element is removed from the cylindrical mold, so that the fine particles of the strain element adhering to the hydrophilic region is firmly fixed.
(7) An electrode is formed on at least one of an obverse surface and a reverse surface of the strain element removed from the cylindrical mold, this is again dipped in the solution containing the suspended fine particles of the strain element having the piezoelectric inverse effect, and is pulled up, so that a laminated coil-shaped strain element including the interposed electrode can be manufactured.
(8) While fine particles of a strain element having a piezoelectric inverse effect are laminated in a vessel, laser light is irradiated to melt and sinter the fine particles of the strain element, so that strain elements of various shapes, such as a strain element wound like a coil, or a strain element wound like a spring, can be manufactured.